The invention generally relates to imaging systems, and relates in particular to imaging systems that employ an illumination modulator.
Imaging system such as those disclosed in U.S. Pat. No. 6,433,934, may include an illumination source, a field lens system, an illumination modulator, imaging optics and an imaging surface. During imaging, the field lens system directs the illumination field onto the light modulator and the light modulator reflects the illumination field toward the imaging surface in one mode and reflects the illumination field away from the imaging surface in another mode. For example, the modulator may include a Grating Light Valve (GLV) as sold by Silicon Light Machines of Sunnyvale, Calif., and the system may direct via the imaging optics either the zero order reflection or the first order reflection toward the imaging surface in various embodiments.
Many imaging systems employ an illumination field that is generally in the shape of a line of illumination, permitting a line of picture elements (or pixels) to be imaged simultaneously. It has been discovered, however, that the performance of certain modulators may change over time, which may cause detrimental effects to the overall system.
U.S. Pat. No. 6,479,811 discloses a system and method for calibrating an illumination modulator that involves sensing illumination from a non-imaging order (e.g., +1st order as shown in FIGS. 7 and 8) at a segmented detector 76. Although such as a system may be employed during imaging, additional optics and control equipment are required for such a system.
There is a need, therefore, for a system and method for efficiently and economically determining whether the performance of a light modulator has changed.